There is known a single crystal pulling apparatus utilizing an MCZ (magnetic-field-applied Czochralski) method in which a crucible melting a single crystal material (particularly, a semiconductor single crystal material) is contained inside a pulling furnace, and a superconducting magnet device is disposed outside the pulling furnace. A magnetic field is applied to the single crystal material which is melted inside the crucible by the superconducting magnet device to thereby prevent convection of the melted single crystal material.
When producing a silicon single crystal using the MCZ method, in many cases, the shape and size of a super-conducting magnet device for applying a magnetic field is restricted in order to prevent mechanical interference with a pulling apparatus. In particular, relatively strict attention must be paid to the connection between the upper end face of the superconducting magnet device and the pulling apparatus main body (for example, pulling machine). Further, when taking into consideration the workability and safety of an operator performing operations on the upper end face, the arrangement of projecting parts such as a refrigerator and a current lead terminal requires a lot of attention.
According to a superconducting magnet device for a single crystal pulling apparatus 100 disclosed in Patent Document 1 (Japanese Patent Laid-Open Publication No. 2004-51475) shown in FIG. 13, a cryogenic refrigerator 102 and a current lead terminal 103 and the like that exist on a cylindrical cryostat 101 are arranged together on a refrigerator port 104 so as to avoid the interference with the pulling apparatus main body.
Further, according to a superconducting magnet device for a single crystal pulling apparatus 110 disclosed in Patent Document 2 (Japanese Patent Laid-Open Publication No. 2000-114028) shown in FIG. 14, a cryogenic refrigerator 102 and a current lead terminal 103 are mounted on a lower end face 112 of a cylindrical cryostat 101 in a manner such that an upper end face 111 of the cryostat 101 forms completely flat surface. Patent Document 3 (Japanese Patent Laid-Open Publication No. 11-199366) also discloses a superconducting magnet device for a single crystal pulling apparatus of the same kind as that disclosed in Patent Document 2.
In comparison with the superconducting magnet device for a single crystal pulling apparatus 100 disclosed in the Patent Document 1, the aforementioned superconducting magnet device for a single crystal pulling apparatus 110 disclosed in the Patent Document 2 is superior with respect to interference with the pulling apparatus main body at the upper end face 111 of the cryostat 101 as well as the workability and safeness in working of the operator.
However, the cryogenic refrigerator 102 requires periodical maintenance, and it is necessary to secure a maintenance space of 800 mm or more in the vertical direction from the installation surface in order to withdraw the refrigerator. Therefore, according to the superconducting magnet device 110 disclosed in the Patent Document 2 in which the cryogenic refrigerator 102 is inserted from the lower end face 112 of the cryostat 101, leg portions 113 are provided to secure maintenance space on the lower end face 112.
In general, with a cylindrical superconducting magnet device for a single crystal pulling apparatus, after the superconducting magnet device is mounted to the single crystal pulling apparatus, the superconducting magnet device is raised and lowered in the vertical direction in order to adjust the magnetic field that is applied thereto. Therefore, if the overall height dimensions of the apparatus are large, the margin for adjustment of the magnetic field decreases.